Leather



United States Patent 3,006,177 LEATHER Norman Limon Holmes, Beverley,and Peter Bryan Curtis, Harrow-Weald, England, assignors to RichardHodgson & Sons Limited, London, England, and The General ElectricCompany Limited, London, England, both British companies No Drawing.Filed Oct. 21, 1958, Ser. No. 768,536 Claims priority, application GreatBritain Oct. 22, 1957 14 Claims. (Cl. 69-21) This invention relates tothe preparation of leather for moulding or other manipulative operation.

In the preparation of leather for moulding or other manipulativeoperation, the conventional practice is to soak the leather in water inorder to render it sufficiently pliant. After, for example, moulding,the leather must then be dried in order to set it permanently in theshape to which it has been moulded. Again, for example, sole leatherwhich has been softened prior to stitching must be dried thereafter inorder to restore its original more elastic form. Soaking and dryingstages consume a considerable amount of time, and may even affectpermanently and adversely the physical properties of the leather.

An object of the present invention is to reduce the total time necessaryfor the preparation of leather for moulding or other manipulativeoperation, which is reflected in a saving of labour.

A further object of the present invention is to provide a method ofpreparing leather for moulding or other manipulative operation which isdesigned to ensure that the original physical properties of the leatherare retained as far as possible after working.

According to the present invention a method of moulding or otherwisemanipulating leather comprises heating the leather under conditionseffective to ensure that at least part of the combined or bound waterpresent therein is temporarily freed whilst avoiding any appreciableevaporation from the leather, whereby the leather is rendered pliant,moulding or otherwise manipulating the resultant heated leather asrequired, and thereafterallowing the freed water present in the leatherto re-enter into its combined or bound form.

The heating should be rapid and of short duration. It should besuflicient to ensure that the combined or bound water is freed for thepurpose indicated whilst avoiding making the leather too hot to handleconveniently. Under ordinary atmospheric conditions, a temperature ofthe order of 60-90 C., dependent upon the type and condition of theleather, is envisaged.

- It may be advantageous to supplement the atmospheric cooling normallyenvisaged by means of applied cooling means.

The precise manner in which the combined or bound 3,006,177 PatentedOct. 31, 1961 Leather Trades Chemists, 1942, 26, pages 237 to 255, ithas been stated that the combined or bound water present in leather isestimated as slightly over 50% of the hide substance.

The invention is applicable to both non-impregnated and impregnatedleathers, the conventional impregnants comprising fats and waxes. In thelatter instance it is of course necessary that the leather is heated toan extent suflicient to soften the thermoplastic impregnant used asdressing. No amount of bound or combined water liber-' ated will enableleather to be moulded or otherwise manipulated if any rigid impregnantassociated therewith is not rendered plastic. 0n the other hand, it hasbeen established that in the presence of an impregnant the amount ofbound or combined water which is required to be liberated by the heattreatment in order that the leather shall be capable of being moulded orotherwise manipulated can be reduced. To this extent the liberated boundor combined water and the impregnant are complementary to one anotherbut it is a basic feature of the present invention that the liberationof some bound or combined water is essential to its successfuloperation.

In a preferred form of the invention, dielectric heating is employed,ensuring a substantially uniform temperature throughout the leatherbeing treated. Thus, the

leather may be heated by placing it for a period of, say, from 20seconds to 1. minute in an electric field applied at frequencies of upto 100 megacycles. A frequency in the range of 10 to 50 megacycles ispreferred. A gen- I erator providing a power density ranging between 10leather.

The electric field may conveniently be applied between two parallelplates, on one of which the leather rests. Since the heating frees thecombined or bound water in the leather, it may on occasions beundesirable for the leather to contact both plates because of therelatively high electric conductivity of the freed water, and thereforean air space may be left between the leather and the upper plate. Since,however, the presence of such an air space may assist the evaporation offreed water 3 from the leather, particularly if it is thin, whichevaporanipulative operation of the leather has not been definitely Iestablished. The water may well act as an interstitial lubricant.porarily dissolve or dilute any tanning material which cross linksfibres and this removal of material then allows greater freedom ofmovement. t

The present invention thus involves the novel concept of temporarilyreleasing at least part of the combined or bound water present inleather, so that it may serve to liberate and lubricate the fibreswhilst the leather is subjected to moulding or the like manipulativeoperation, and thereafter allowing the water to re-enter into itscombined or bound state. In an article-entitled The Influence of BoundWater on the Equilibrium in Leather- Water Systems, by A. Cheshire andN. L. Holmes, published in the Journal of the International Society ofAlternatively, or in addition, it may teme tion is to be discouraged, itmay be found expedient to fill the air space with a layer of anelectrically insulating material, such as mica, particularly whenemploying a Warm air blast to keep the plates free from atmosphericcondensation. Further, the leather itself may be coated with a resin orother similar material to prevent loss of moisture.

If the leather is allowed to cool in air after moulding, several minutesmay elapse before the leather has set in the shape to which it has beenmoulded. It may therefore be advantageous to carry out the moulding stepusing a water cooled mould.

The possibility of providing a generator adapted to serve also as apress is envisaged. Thus, the upper electrode may have a formed,insulating face and the two electrodes may be used to mould the leatherto shape after heating.

Some guide to the interrelationship of the moisture content of theleather, the time of heating and the power density will be apparent fromthe succeeding table in the derivation of which specimens ofnon-impregnated dress- 3 ing hide, each measuring approximately 7" by 2/2" and 4 mm. thick, and taken from hides which had been lightly oiledand thereafter subjected to atmospheric drying, were subjected todifferent times and varying intensities of heating. A constant RFvoltage of 5.5 kv. at 20 megacycles was applied to the electrodes.

VISUAL APPEARANCE Weight of Water in Leather (Le. X gms. water/IOO- XAir 'H'Pafi'nn' gms. dry matter) Gap, Time, Ins. Secs.

20 gJlOO g. wet 25 g./l g. wet 30 gJlOO g. wet leather leather leather30 Normal Normal Normal. 60 do do Do. syn.-. 120 do Slight internal D0.

gluclng. Normal Glueing at the centre. .....de Normal. do Do.

Slight sln-lnk- Drawn grain. ing; extract glueing at one en 180 doShrunk; warped Exploded. and charred at one end. 30 d0 Slight shrink-Drawn and ing at one curled up at en one end. 60 .d0 Blown up at D0.

one end. 134'. 120 do Blown up and grain shrunk at both ends. 180 Veryslight ex- Blown up and tract glueing charred at on flesh side. one end.30 Normal 60 -.--.do d 120 Slight extract do glueing on flesh. 180 do d020 gms./ 100 gms. wet leather represents approximately the full combinedor bound water content of the leather under examination and it will beapparent that the presence of free water in cold untreated leather mayleadto damage to the leather on heating for more than quite shortperiods. Thus, generally speaking the upper limit of water present inthe leather must not greatly exceed the extent of the bound waterinherent in the leather. This will vary with the type of tannage but isnormally 50% by weight of the hide substance. Any significant increasein the amount of free water present can very readily lead to rapiddeterioration of the leather.

It is equally important to ensure that the leather is not too dry beforebeing subjected to the heat treatment. Though dependent to some extenton the impregnaut content, leather which is too dry may crack.

Generally speaking, leather can be moulded effectively in accordancewith the present invention if it is in equilibrium With an atmospherehaving a relative humidity of between not less than 30% and not morethan 85%. The following data exemplify typical operating conditionswhich may be encountered in the successful heat treatment of twodifferent types of leather.

(1) Using a 20 megacycle generator supplying 5.5 kv. to electrodespresenting an air gap of 1", then the insertion of a 4 /2" diameter discof impregnated leather of A" thickness (stearic acid as impregnant; 25parts per 100 parts leather) resulted in a temperature rise in theleather of approximately 65 C. above ambient in a time of 30 seconds.

(2) A sample of non-impregnated dressing hide measuring 7 /2 by 2 /2 andbeing A" thick when placed between electrodes presenting an air gap of 1/2" and fed with a voltage of 5.5 kv. at 20 megacycles resulted in atemperature rise of 52 C. in 30 seconds.

It must again be emphasised that these data are included by way ofexemplification only. The optimum conditions for treating any particulartype of leather must be determined by experiment.

The invention is capable of widespread application in the leatherindustry. Thus, the production of saddles for bicycles and horses, fromheavy leathers is envisaged. Again, the invention is likely to find aready application in the treatment of leather intended for soles forfootwear and in the production of moulded uppers for footwear. Thepossibility is envisaged wherein a veldtschoen upper may be. mouldedfrom a softened blank of leather using, for example, a pneumatic bagmoulding technique wherein an inflated rubber diaphragm is employed toblow the leather blank into a wooden negative mould shape.

Again, the invention has obvious application in the production of cupwashers of all descriptions and this particular aspect of the inventionis exemplified in the following two examples.

Example 1.-Meth0d of producing 3" oak tanned cup leather Size offinished cup-33" outside diameter, 1'' deep, thick. Size of circle to becut from leather-5. Thickness- 7 Time for dielectric treatment-35seconds. Time left in mould--2 /z to 4 minutes dependent on type ofleather.

Example 2.2" chrome ram leather Finished size3" outside diameter, 2"inside diameter deep, A thick. Size of circle to be cut from leather-6".Thickness- A Time for dielectric treatment 35 seconds. Time left inmould 2 /2 to 4 minutes dependent on type of leather.

We claim:

1. A method of manipulating leather which comprises heating the leatherunder conditions elfective to ensure that at least part of the boundwater present therein is temporarily freed whilst avoiding anyappreciable evaporation from the leather, whereby the leather isrendered pliant, manipulating the resultant heated leather as required,and thereafter allowing the freed water present in the leather tore-cuter into its bound form.

2. A method of manipulating leather which comprises first adjusting themoisture content of the leather such that it is in equilibrium with anatmosphere of which the relative humidity lies between 30% and heatingthe leather under conditions efiective to ensure that at least part ofthe combined water present therein is temporarily freed whilst avoidingany appreciable evaporation from the leather, whereby the leather isrendered pliant, manipulating the resultant heated leather as required,and thereafter allowing the freed water present in the leather tore-enter into its combined form.

3. A method of manipulating an impregnated leather which comprisesheating the leather under conditions effective to ensure that at leastpart of the bound water present therein is temporarily freed whilstavoiding any appreciable evaporation from the leather and that theimpregnant is softened, whereby the leather is rendered pliant,manipulating the resultant heated leather as required and thereafterallowing the freed water present in the: leather to re-enter into itsbound form and allowing the impregnant to harden.

4. A method of moulding leather which comprises subjecting the leatherto dielectric heating in order to libcrate temporarily at least part ofthe bound water present in said leather whilst avoiding any appreciableevaporation, whereby the leather is rendered pliant, moulding theresultant heated leather as required, and thereafter allowing the freedwater present in the leather to re-enter into its bound form.

5. A method of moulding an impregnated leather which comprisessubjecting the leather to dielectric heating efiective to liberatetemporarily at least part of the bound water present in said leatherwhilst avoiding any appreciable evaporation and to soften theimpregnant, whereby the leather is rendered pliant, moulding theresultant heated leather as required, and thereafter allowing the freedwater present in the leather to re-enter into its bound form andallowing the impregnant to harden.

6. A method of moulding leather which comprises first ad usting themoisture content of the leather such that it is in equilibrium with anatmosphere of which the relative humidity lies between 30% and 85%,subjecting the leather to dielectric heating in ,order to liberatetemporarily at least part of the bound water present in said leatherwhilst avoiding any appreciable evaporation, whereby the leather isrendered pliant, moulding the resultant heated leather as required, andthereafter allowing the freed water present in the leather to re-enterinto its bound form.

7. A method of moulding leather which comprises supporting the leatherbetween the electrodes of a dielectric heating apparatus, applying anelectric field between the electrodes at a power density ranging betweenand 100 watts per cubic inch of leather and a frequency lying within therange 10 to 100 megacycles for a period of time of from 20 seconds to 1/2 minutes in order to heat the leather and thereby render it pliant,moulding the resultant heated leather, and thereafter allowing theworked leather to cool and permanently set in its moulded shape.

8. A method as claimed in claim 7 in which the frequency is 20megacycles.

9. A method of moulding leather which comprises supporting the leatheron the lower of a pair of parallel plate electrodes forming part of adielectric heating apparatus, interposing an electrically insulatingmaterial between the leather and the upper electrode, applying anelectric field between the electrodes at a power density ranging between10 and 100 watts per cubic inch of leather and at a frequency lying inthe range 10 to 100 megacycles for a period of time of from 20 secondsto 1 /2 minutes in order to heat the leather and thereby render itpliant, moulding the resultant heated leather and thereafter allowingthe worked leather to cool and permanently set in its moulded shape.

10. A method of moulding leather which comprises supporting the leatherbetween the electrodes of a dielectric heating apparatus, applying anelectric field between the electrodes at a power density ranging between10 and 100 watts per cubic inch of leather and at a frequency in therange 10 to 100 megacycles for a period of time of from 20 seconds to 1/2 minutes in order to heat the leather and thereby render it pliant,moulding the resultant leather by pressing it between the electrodes andthereafter allowing the pressed leather to cool and permanently set inits moulded shape.

11. A method of manipulating leather which comprises temporarilyreleasing at least part of the combined water present in the leather sothat it may serve to liberate and lubricate the fibres by subjecting theleather to dielectric heating, whereby the leather is rendered pliant,manipulating the resultant heated leather as required, and thereafterallowing the worked leather to regain its original physical state.

12. A method of moulding leather which comprises placing said leather inan electric field applied at a frequency lying within the range 10 tomegacycles until the leather becomes hot and pliant, manipulating thepliant leather to a predetermined shape and thereafter allowing theleather to cool in order to retain said shape.

13. A method of making leather cup washers which comprises placing adisc of leather in an electric field applied at a frequency lying withinthe range 10 to 100 megacycles until the leather becomes hot and pliant,manipulating the pliant leather disc into cup shape and thereafterallowing the leather to cool in order to retain said shape.

14. A method of moulding leather which comprises coating one surface ofthe leather with a resin to prevent loss of moisture from that surface,supporting the leather on the lower electrode of a dielectric heatingapparatus with the coated surface uppermost, applying an electric fieldbetween the electrodes at a power density ranging between 10 and 100watts per cubic inch of leather and a frequency lying within the range10 to 100 megacycles for a period of time of from 20 seconds to IV:minutes in order to heat the leather and thereby render it pliant,moulding the resultant heated leather, and thereafter allowing theworked leather to cool.

References Cited in the file of this patent UNITED STATES PATENTS2,321,131 Crandell June 8, 194

2,619,661 Hart Dec. 2, 1952 2,644,966 Juhola July 14, 1953 FOREIGNPATENTS 113,232 Australia May 30, 1941 608,537 Great Britain Sept. 16,1948

